[FIX] web_editor: write with string in update_checklist

Before this commit, when the user tried to update a checklist, there
was a traceback in `handle_history_divergence` because the `value` is a
byte sequence instead of a string.

opw-3158660
task-3165844

closes odoo/odoo#112098

X-original-commit: e3900dfe
Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>

addons/web_editor/controllers/main.py

@@ -175,7 +175,7 @@ class Web_Editor(http.Controller):
         else:
             return value
 
-        value = etree.tostring(htmlelem[0][0], encoding='utf-8', method='html')[5:-6]
+        value = etree.tostring(htmlelem[0][0], encoding='utf-8', method='html')[5:-6].decode("utf-8")
         record.write({filename: value})
 
         return value